Probably because the 40 is loaded hotter than the 45. There are many studies on the subject and not all of them agree with each other. Yes, loaded to the same fps a 230 will have more recoil than a 185 from the same gun. But that's only a small part of the equation. Powder burn rate, charge weight, loaded round length ie seating depth, and some other esoteric things will all have a effect. You cant beat the laws of physics (at least not yet). Internal and external ballistics are very interesting and would take thousands of pages to cover. Search engines are your friend.

 

^^^^^ What he said ^^^^^^

 

Subjectively... My G21 has less felt recoil with a 230 gr load of any flavor than the 200 gr Hornady loads I was carrying. They were standard pressure, but the 200 gr load to me felt snappier, while the 230 gr was more "pushy".

 

As alluded to above, the specific load used will affect felt recoil. For example, when I was experimenting with .38 Special loads, I achieved similar velocities with the same 158 gr bullet using both Titegroup powder and Unique. But the Titegroup has a faster burn rate and appears to develop peak pressure faster than the Unique, and its recoil was decidedly "snappier" than that of the Unique loads generating the same muzzle velocity.

Remember that recoil force is delivered over a period of time. If you drew a graph of the recoil force over time, the total recoil impulse is the area under the curve. A high force over a short duration can have the same recoil impulse as a lower force over a longer duration, but the latter will seem far easier for the shooter.

 

I don't remember the bullet weight of each but I saw a video test measuring the angle of recoil when comparing 9mm, 40 and 45. The 9 caused the least jump as expected (measured in degrees), next, not so predictable was the 45. The 40 moved the meter the most with a gap almost as wide between it and the 45 as between the 9 and the 45. So, biggest jump was between 9 and 45 but the 40 was significantly ahead of the pack. That data confirms what I feel when shooting them. I have shot a ton of 40 and 9mm but just a little of the 45s as I've been researching a new addition.

I am only guessing (old age memory ) but it seems the 9 caused about a 27 degree jump, the 45 was around 33 degrees and the 40 was 37 or so. Maybe someone else can provide the exact numbers.

 

If EVERYTHING else were constant, the heavier bullet should transmit more recoil to the shooter. But the other possible variables are virtually NEVER the same.
For one thing, each individual can perceive the same amount of recoil differently. Some folks can tolerate much more recoil than others. Some people are especially sensitive to recoil, and need the softest shooting gun they can get. The gun's design and materials will significantly effect perceived recoil. Frame material, gun weight, grip size, bore axis, grip angle all play a part, as does bullet weight, powder charge, burn rate.

While generalizations can be made, IMO, the only way for an individual to determine perceived recoil is to shoot the gun in question with the ammunition in question.

FYI, here are some caliber recoil figures from "Ammo and Ballistics 3":

.380/9mm Makarov: .41
.38 Special: .53
9x19: .65
.40S&W: .74
.357SIG: .76
.357Magnum: .89
.45ACP: .93

But to me, .45ACP feels like it has less recoil than .357Magnum. And many .380 semi-autos are of blowback design, which I feel absorbs less recoil than the locked breech design of most 9mm's. So to me, shooting a .380/9mm Makarov, feels similar to a locked breech 9x19 of similar size and weight.

 

Again, those referenced numbers for recoil are one-dimensional, whereas recoil is a force delivered over time. Your comment about .45 vs. .357 is spot on and illustrates the point.

farsidefan1, if you're looking into a .45, please don't let recoil keep you from considering the caliber! You know you're shooting something, but it's far from objectionable.

 

In most cases, at least with factory ammo, the lighter ammo can tend to recoil more, although it can depend on the cartridge (like 9mm vs 9mm +P) and really the pressures it's loaded, but sometimes the heavies can recoil a little more. Less bullet weight might make you think it will recoil less, but that just makes more room for powder and higher velocity, which also increases recoil and blast, and some do mistake extra blast for more recoil too as it can sometimes have a concussive effect (esp with the .357 mag whose recoil isn't that bad, but it's muzzle blast can be heavy).

This afternoon I was shooting and chronographing some ammo, handloads and factory ammo and out of the G17 I ran 115gr Blazer Brass, 147gr Federal HST, 135gr +P Hornady Critical Duty, 124gr +P Speer Gold Dot and 115gr +P+ Federal 9BPLE. I listed them in that order because that's what recoiled from least to the most, with the regular pressure 115gr and 147gr being very similar (slightly more with 147gr but I think they were loaded a little warm whereas the 115gr Blazer isn't warm at all), and the +P's recoiling more, except the 135gr +P was only slightly more than the 147gr, as it only averaged 40 fps faster.

All of those recoiled rather mildly compared to a handload shooting a 200gr WFNGC hardcast out of a 6" G24 (G24 KKM bbl in a G35) at almost 1,280 fps avg, that's nearly as fast (within 25 fps) as the factory Federal 115gr +P+ out of the G17, with a bullet weighing nearly twice as much.